Allow validation of CONFIG files

[geographika]

And add these to https://mappyfile.geographika.net/
Quickly find cause of getString(): Symbol definition error. Parsing error near (:):(line 4) (in this case due to an extra quote).

CONFIG
  ENV
        MS_MAP_PATTERN "."
	PROJ_LIB" "C:/MapServer/bin/proj7/SHARE"
  END
END

[geographika]

SYMBOLSET files are already supported by the parser - see code at:

mappyfile/mappyfile/mapfile.lark

Line 30 in e153820

start: "SYMBOLSET"i composite_body _END -> symbolset

For parsing a MapServer CONFIG file (see https://mapserver.org/mapfile/config.html) a new test branch has been created at: https://github.com/geographika/mappyfile/tree/config-parser

The current approach is to create a separate grammar file - https://github.com/geographika/mappyfile/blob/config-parser/mappyfile/configfile.lark

A new parameter is then passed to the Parser:

mappyfile/mappyfile/parser.py

Line 75 in a715379

is_config: bool = False,

Keeping the grammars separate seems to make sense as the two files have different keywords and purposes. The Transformer however is reused.
Selecting the correct grammar file could perhaps be automated by checking the first string value in input file?

There are a few issues in the current branch around strings and quoting. All CONFIG examples seem to have the keywords unquoted, so perhaps only this should be supported. All values should be quoted.